It is known in the art relating to diesel engines to provide a fabricated crankcase including individual cylinder head retainers in which cylinder heads with attached cylinder liners are received and by which they are supported. A seat ring or wear ring of bearing material, such as bronze, is commonly provided at the joint where the cylinder head flange is supported on an upper surface of the cylinder head retainer. The seat ring is a replaceable wearing member that provides for any wear which may occur and seals against the leakage of oil into or gases out of the exhaust system passages located below the seat ring in the cylinder head and crankcase.
In certain engine constructions, lubricated camshaft and rocker mechanisms above the cylinder head and engine top deck discharge oil which runs along the upper crankcase walls and around the edges of the head seat ring from a sloping extension of the head retainer, thereby carrying the oil against the cylinder head to retainer joint.
Experience has shown that wear of the seat ring has most commonly occurred in the area above the cylinder head and crankcase exhaust passages, that is, the area at the upper edge of the sloping joint surface against which the lubricating oil returning to the engine sump is inclined to flow. Thus, where excessive wear of the seat ring has occurred, leakage of oil into the exhaust system and "souping" of the engine exhaust has sometimes resulted.
In a previous method of meeting this problem in some engines, an O-ring seal has been installed on each cylinder head at the juncture of the cylinder head body and flange, immediately above the cylinder head seat ring. While this modification has likely reduced the extent of the problem, the installation of the seal together and the seat ring together with the cylinder head and liner assembly has proved somewhat difficult and not always satisfactory in that pinching or mislocation of the seal may result. In addition, even if the O-ring seal is properly applied, its effect is to seal only the upper joint of the seat ring to cylinder head flange, allowing the possibility that some leakage may still occur between the lower surface of the seat ring and the cylinder head retainer upper surface.